1. Technical Field
The present invention relates to a metal plate for electromagnetic heating, and more particularly to a metal plate for electromagnetic heating which is advantageously employed for receptacles for use in cooking utensils, particularly in cooking utensils of electromagnetic heating type. The present invention also relates to a method of manufacturing the metal plate for electromagnetic heating.
2. Description of Related Art
Conventional receptacles for use in cooking utensils of electromagnetic heating type, such as a bowl placed within a rice cooker, include as substrate thereof a composite plate formed of a magnetic metal plate such as iron or stainless steel which serves to generate heat and an aluminum or aluminum alloy plate which serves to conduct heat, and have been manufactured by subjecting the composite plate to press forming, such as deep drawing, with the latter plate being positioned inside. Generally, the substrate is further provided with fluororesin coating on its inner surface to prevent rice sticking and the others.
Composite plates for the substrate have been heretofore manufactured by a method wherein a magnetic plate and an aluminum or aluminum alloy plate are clad (combined) by roll forming, such as those disclosed in Japanese Kokoku Patent Nos. Sho 54-3468 and Sho 54-9985. As such, the conventional composite plates have been manufactured by means of a cladding method incorporating a roll forming and are accordingly suitable for mass production thereof.
The conventional composite plates, such as those described above, however have a drawback that a wide range of variations in thickness thereof takes place because they are manufactured by means of roll forming and an aluminum or aluminum alloy plate is subjected to press-bonding. This frequently causes a clad plate to crack or wrinkle when it is pressed, and accordingly imposes a serious processing problem. For the conventional composite plates, the magnetic metal plate such as comprising iron or stainless steel for serving to generate heat and the aluminum and aluminum alloy plate for serving to conduct heat are both required to be highly extensible and also capable of withstanding rolling and forming processings, which brings about another problem of giving more factors to limit a range of material selection.
In recent years, recycling materials has been regarded as very important to effectively use industrial resources. In accordance with the clad method incorporating a roll forming process, the magnetic metal plate and the aluminum or aluminum alloy plate are clad to produce the composite plate which is subsequently punched to leave the same of predetermined shape and consequently produces a large volume of scraps formed of the composite material. Contrary to a recyclable single metal plate such as an aluminum or aluminum alloy plate, those scraps of the composite material are not recyclable, which increases a manufacturing cost of the composite metal plates Furthermore, the clad method finds difficulties in manufacturing a composite metal plate incorporating a magnetic metal plate exclusively in a portion required for heat generation.